President Donald Trump is expected to nominate Kirstjen Nielsen to run the Department of Homeland Security, possibly as soon as Wednesday, according to two administration officials and three outside advisers familiar with the process.

Nielsen served as White House chief of staff John Kelly’s top aide during his time as DHS secretary and moved with him to the West Wing as his principal deputy chief of staff when he was appointed in July, leaving the Cabinet post vacant.

The White House didn’t immediately comment. Nielsen did not respond to a request for comment.

People familiar with the search cautioned that, as with everything in the Trump White House, nothing is final until it’s publicly announced.